1. Technical Field
The present invention relates generally to paving material density analyzers. More particularly, the present invention relates to a paving material analyzer system and a method for analyzing paving material. The invention also relates to mechanisms for improving the accuracy of a paving material analyzer system and method.
2. Related Art
During paving operations, paving material is usually laid at about 75% of acceptable compaction. Acceptable compaction is a recommended level of compaction that reduces variations in the material, such as air voids, that can create potential defects in the paving material. It is highly advantageous to compact the paving material to a level as close to acceptable compaction as possible. Unfortunately, the level of compaction is not readily apparent by viewing the compacted paving material. In order to address this problem, measurement of dielectric properties of paving material is known to be very useful for determining material density, a key indicator of compaction level.
One pavement density indicator device is that of Blackwell, U.S. Pat. No. 3,784,905. Blackwell""s device measures dielectric properties of the asphalt, which is representative of the change in density in the asphalt. The device of Blackwell has many disadvantages. For example, in order to obtain a reading, the Blackwell device must be moved at extremely slow speeds across the material being tested and, accordingly, requires an extended time period to provide a determination. The Blackwell device, due to its excessive weight, also requires a large sled frame (contact area) to be dragged across the pavement surface. Another disadvantage is limited adjustability of the depth of measurement of the device caused by the given set of electrodes only being able to vary the depth of measurement by changing the height of the electrodes. Yet another disadvantage is the inability to measure density when the paving material is wet.
In another apparatus, a nuclear source is used to determine density of pavement material. This device has a variety of obvious drawbacks. For instance, the device requires a licensed operator and a radiation shield (e.g., a lead enclosure). Furthermore, the device is non-adjustable for area, time-consuming in use, and heavy.
Another disadvantage of the above-described devices is their inability to vary the shape and area of the sensing area. Altering the shape and area of the sensing area is advantageous for determining the density in particular pavement attributes, e.g., dips, joints, odd shaped patches, etc.
Yet another disadvantage of the above-described devices is that their operation speed is relatively slow. It is therefore desired to have a system which is faster than those available.
Another shortcoming of current devices is inaccuracy created by, among other things, moisture on a surface of the paving material and a standoff distance of the sensor from the paving material surface.
In view of the foregoing there is a long felt need for a reliable paving material analyzer system and method for analyzing paving material. There is also a need for a system and method that can correct for moisture on the paving material. In addition, there is a need in the art for a system and method having increased accuracy.
The invention overcomes the above shortcomings by providing in a first aspect of the invention, a paving material analyzer system comprising: a sensor; an electronic circuit operatively coupled to the sensor to generate an electrical field from the sensor proximate the paving material; and a data analyzer that determines a density of the paving material based on the effect of impedance characteristics of the paving material on the electrical field.
A second aspect of the invention provides a method for analyzing paving material comprising the steps of: determining an impedance of the paving material; and determining the density of the paving material based on the impedance determination of the paving material.
A third aspect of the invention provides a paving material analyzer system comprising: means for determining an impedance of the paving material; and means for determining the density of the paving material based on the impedance determination of the paving material.
In a fourth aspect of the invention is provided a paving material analyzer system comprising: a sensor; an electronic circuit operatively coupled to the sensor to generate an electrical field from the sensor proximate the paving material; and a density determining data analyzer that determines a density of the paving material regardless of moisture presence on the paving material.
A fifth aspect of the invention is directed to a paving material analyzer system comprising: an electronic circuit including an inductor adapted to null a capacitive reactance portion of an impedance reading of the paving material leaving a non-reactive portion; and a data analyzer operatively coupled to the electronic circuit that determines: a total impedance of the paving material based on the non-reactive portion, a known inductive reactance and a known operating frequency of the electronic circuit, and a density of the paving material based on the total impedance.
A sixth aspect of the invention is directed to a paving material analyzer system comprising: means for measuring an impedance of the paving material and nulling a capacitive reactance portion of the impedance; means for analyzing data operatively coupled to the means for measuring, the means for analyzing determining: a total impedance of the paving material based on a non-reactive portion of the impedance, a known inductive reactance portion of the impedance and a known operational frequency of the means for measuring, and a density of the paving material based on the total impedance.
A seventh aspect of the invention provides a method for analyzing paving material comprising the steps of: determining an impedance of the paving material; determining a capacitance of a space between a sensor and the paving material; and determining the density of the paving material based on the impedance determination of the paving material and the capacitance of the space.
An eighth aspect of the invention is directed to a paving material analyzer system having a sensor operatively couple to an electronic circuit for generating an electric field proximate paving material and a data analyzer for determining a density of the paving material, the system comprising: a standoff distance corrector that corrects the density for a distance of the sensor to the paving material.
The foregoing and other features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention.